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The selective binding of six ( S )-quinuclidine-triazoles and their ( R )-enantiomers to nicotinic acetylcholine receptor (nAChR) subtypes α3β4 and α7, respectively, were analyzed by in silico docking to provide the insight into the molecular basis for the observed stereospecific subtype discrimination. Homology modeling followed by molecular docking and molecular dynamics (MD) simulations revealed that unique amino acid residues in the complementary subunits of the nAChR subtypes are involved in subtype-specific selectivity profiles. In the complementary β4-subunit of the α3β4 nAChR binding pocket, non-conserved AspB173 through a salt bridge was found to be the key determinant for the α3β4 selectivity of the quinuclidine-triazole chemotype, explaining the 47-327-fold affinity of the ( S )-enantiomers as compared to their ( R )-enantiomer counterparts. Regarding the α7 nAChR subtype, the amino acids promoting a however significantly lower preference for the ( R )-enantiomers were the conserved TyrA93, TrpA149 and TrpB55 residues. The non-conserved amino acid residue in the complementary subunit of nAChR subtypes appeared to play a significant role for the nAChR subtype-selective binding, particularly at the heteropentameric subtype, whereas the conserved amino acid residues in both principal and complementary subunits are essential for ligand potency and efficacy.

Lung cancer, one of the most commonly found carcinoma type, has the highest mortality rate in cancer patients worldwide. Therapeutic interventions targeting to lung cancer become remaining the world significant challenge. Recently, the α7-nicotinic acetylcholine receptor (α7-nAChR) was reported to play an important role in the mechanism underlying lung cancer progression, being intriguing drug target for lung cancer therapy. Hence, the top four α7-nAChR antagonists (QND7, PPRD10, PPRD11 and PPRD12) among our previously developed ligands were proceeded to the in vitro anti-cancer evaluations in non-small cell lung cancer (NSCLC) cell lines (H460 and A549). In this study, we found that QND7 exhibited the highest cytotoxic effect and induced cell apoptosis in both cell lines at a level comparable to cisplatin, whereas the PPRD compounds showed much lower cytotoxicity. Low doses of QND7 and PPRD11 were able to suppress H460 and A549 cell proliferation, whereas PPRD10 and PPRD12 were considered ineffective. In an in vitro wound healing assay, QND7-treatment showed the greatest suppression of H460 and A549 cell migration. The variations in the anti-cancer activities of PPRD compounds might be, at least in part of, their non-selective antagonisms to serotonin receptor (5-HT3) and α4β2-nAChR. Further investigation revealed that QND7 was able to minimize protein kinase B/mammalian target of rapamycin (Akt/mTOR) activity, in correlating to its anti-cancer effects. These findings warrant QND7 for further preclinical evaluation and demonstrate the potential of α7-nAChR as cancer drug target., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Three series of substituted anti-1,2,3-triazoles (IND, PPRD, and QND), synthesized by cycloaddition from azide and alkyne building blocks, were designed to enhance selectivity and potency profiles of a lead α7 nicotinic acetylcholine receptor (α7-nAChR) agonist, TTIn-1. Designed compounds were synthesized and screened for affinity by a radioligand binding assay. Their functional characterization as agonists and antagonists was performed by fluorescence resonance energy transfer assay using cell lines expressing transfected cDNAs, α7-nAChRs, α4β2-nAChRs, and 5HT3A receptors, and a fluorescence cell reporter. In the IND series, a tropane ring of TTIn-1, substituted at N1, was replaced by mono- and bicyclic amines to vary length and conformational flexibility of a carbon linker between nitrogen atom and N1 of the triazole. Compounds with a two-carbon atom linker optimized binding with Kd's at the submicromolar level. Further modification at the hydrophobic indole of TTIn-1 was made in PPRD and QND series by fixing the amine center with the highest affinity building blocks in the IND series. Compounds from IND and PPRD series are selective as agonists for the α7-nAChRs over α4β2-nAChRs and 5HT3A receptors. Lead compounds in the three series have EC50's between 28 and 260 nM. Based on the EC50, affinity, and selectivity determined from the binding and cellular responses, two of the leads have been advanced to behavioral studies described in the companion article (DOI: 10.1021/acschemneuro.5b00059).